1. Field of the Invention
The present invention relates to a method and apparatus for forming an image on a recording medium. More specifically, the present invention relates to a method and apparatus for forming an image on a recording medium having expansion/contraction properties such as a cloth. The present invention also relates to a method and apparatus for forming an image by emitting ink using an ink-jet head according to an ink-jet recording technique.
2. Description of the Related Art
An ink-jet recording apparatus is widely used because of its ease of use. In this type of recording apparatus, recording is accomplished by emitting ink toward a recording medium.
The ink-jet recording apparatus includes an ink-jet head for emitting an ink droplet and an ink tank for storing ink to be supplied to the ink-jet head. The ink-jet head has an emission orifice through which ink is emitted. Near the emission orifice, there is provided an emission energy generator used to emit ink. Various types of energy generators are known. They include a heat generator for applying thermal energy to ink and a piezoelectric device for applying a mechanical pressure to ink thereby emitting the ink. The ink tank is connected to the emission orifice via an ink flowing path.
In recent years, image forming apparatus for printing an image on a cloth according to an ink-jet technique is used. In this type of textile printing system, unlike conventional screen textile printing systems, it is not required to prepare a master image to be printed. Therefore, this type of textile printing system has the advantage that a wide variety of images can be printed and the total printing cost is low.
However, both the ink-jet textile printing system and the screen textile printing system have a common problem that expansion/contraction or deformation of a cloth during a printing process can cause a printed image to have distortion. This problem is described in further detail below for both textile printing systems.
(1) Screen Textile Printing System
In screen textile printing systems, a printing belt having a flat surface with a size as large as 10 to 30 meters is used to move a plurality of screen frames up and down in a vertical direction thereby forming a color image on a cloth. The cloth on which the image is to be printed is stuck via an adhesive material onto the printing belt using a cloth expanding and sticking apparatus. It is generally required that bending and skewing during the expanding and sticking process should be less than 3%. To meet the above requirement, the bending/skewing of the cloth is corrected using a cloth bending/skewing correcting apparatus before the cloth is supplied to the cloth stretching apparatus. However, the highest available correction accuracy is 1% to 3%. This rather low correction accuracy causes printed images to have distortion.
(2) Ink-Jet Printing System
An example of an ink-jet printing system is disclosed in Japanese Patent Laid-Open No. 5-212851. In this type of textile printing system, as can be seen from the description and the drawing of the patent cited above, in particular from FIG. 2 thereof, printing is performed by emitting ink from an ink-jet head toward a cloth employed as a recording medium being moved in a vertical direction. The system has a printing section for emitting ink. The printing section includes a printing unit provided with an ink-jet head and also includes a conveying mechanism including an endless belt or a conveying belt made of metal wherein the printing unit and the conveying mechanism are disposed at locations opposing each other via a cloth.
An adhesive layer is provided on the surface of the conveying belt so that the cloth can be stuck in a flat fashion on the conveying belt via the adhesive layer. The conveying belt is driven such that it rotates intermittently so as to intermittently convey the cloth by a predetermined distance at a time.
An image is printed on the surface of the cloth along one printing line at a time using a known serial printing technique. After completion of the printing, the cloth is pulled by a proper tension applied by a wind-up roller disposed at an extremely downstream location on the conveying path. At the end of the conveying belt, the cloth is separated from the adhesive layer and wound around the wind-up roller via a cloth path.
In ink-jet printing systems including the specific example described above, a crease-preventing roller is generally used to prevent the cloth from having creases when the cloth is stuck onto the adhesive layer of the conveying belt. This causes the cloth to have a nonuniform tension. As a result, the cloth stuck to the conveying belt has distortion. In order to improve the sticking accuracy to the adhesive layer, it is required to expand the cloth in a particular direction. If an image is printed on the expanded cloth, the aspect ratio of the image will become incorrect when the cloth is released from the expansion.
In the conventional screen textile printing system, as described above, it is known to use a cloth bending/skewing correcting apparatus to correct the bending/skewing of a cloth. However, about 3% distortion occurs in commonly-used apparatus and about 1% distortion occurs in highest-performance apparatus. As a result, the image printed on the cloth always has distortion. In order to precisely feed a cloth without creating distortion in printed images using the conventional screen textile printing apparatus in which distortion of the cloth is mechanically corrected, complicated mechanisms and/or troublesome manual operations by a human operator are required. In practice, therefore, printed images have a ceratin amount of distortion.
The distortion of the recording medium can cause a serious problem in particular when an image is formed via a plurality of image forming processes using various types of dyes as is the case with the textile printing on a mixed fabric. In such textile printing processes, distortion occurs not only in an image formed first but also in an image formed later. The distortion in the images can cause the images to be shifted from each other. Thus, an image miss registration or an undesirable nonuniformity can occur.
In the textile printing on a cloth, an image formed on the cloth is fixed by impregnating a coloring agent such as a dye contained in ink into fibers. When the cloth has a large thickness, it is required to impregnate a larger amount of dye into fibers. In general, the proper amount of dye impregnated into fibers is determined by visually observing the back side of the cloth on which no image is printed to check whether the dye reaches the back side.
In the art of the textile printing, it is desired to form an image on a cloth such that the image can be viewed from both sides thereby increasing the value of the cloth in markets. In particular for cloths such as a handkerchief and a scarf or for a decorating cloth such as a curtain, an image on a cloth is viewed from both sides in most cases and thus it is desirable that images be formed on both sides by increasing the amount of dye which reaches the back side in such a manner that the images on both sides correspond to each other.
One possible technique to increase the amount of dye present on the back side is to print an image on both sides of a cloth. However, in practice, it is very difficult to print an image on both sides in the ink-jet textile printing technique and also in the screen textile printing technique. In particular, it is not known to form images on both sides such that the images formed on the respective sides are coincident with each other. Some methods of printing images on both sides of a cloth are described below. However note that these methods are not good enough.
(1) A Dye having a High Penetration Property is Employed so that the Dye can Reach the Back Side
This technique is limited to cloths having a small thickness. Another problem of this technique is that the high penetration property of the dye causes an image formed on a cloth to feather. If the feathering is suppressed, the dye cannot reach the back side of the cloth. Furthermore, when the cloth has a large thickness, the dye cannot reach the back side and thus it is impossible to form an image on both sides.
(2) First, Coloring (Dip Dyeing) is Performed Over the Entire Coth
Then decoloring is performed on the colored cloth in accordance with a pattern to be printed as the pattern is printed with ink containing a dye which cannot be decolored by the decoloring agent employed. In this technique, only one color of image formed by means of dip dying can be printed such that it uniformly reaches the back side. Other colors will have the same problems as those in the technique (1). Another problem of this technique is that it is required to properly select a dye capable of being decolored and a dye incapable of being decolored. That is, the types of dyes are limited and thus all dyes capable of providing a desired color cannot be used. An alternative possible technique is to print an image on both sides of a cloth. However, as will be described below, this technique has the problem that it is difficult to form high-quality images on both sides in a desirable fashion.
(3) Images are Formed on Both Sides Using a Screen Textile Printing Technique
In this technique, an image is first printed on the principal surface of a cloth and then another image is formed on the back surface of the cloth turned over. However, when the coth is turned over after the image is printed on the principal surface of the cloth, the cloth is expanded or contracted in a manner different from the manner in which the cloth is expanded or contracted when the image is printed on the principal surface. That is, there is a difference in distortion between printing processes for the principal surface and for the back surface. As a result, the resultant images formed on both sides become inconsistent with each other.
(4) Images are Formed on Both Sides Using an Ink-jet Textile Printing Technique
For recording media having substantially no expansion/contraction properties such as a film, it is possible to print images on both sides at the same time using a technique disclosed for example in U.S. Pat. No. 5,376,957. However, a recording medium having expansion/contraction properties such as a cloth cannot be conveyed while maintaining a high accuracy using a pair of rollers disclosed in the patent cited above. That is, nonuniformity of the cloth on the band causes nonuniformity in the resultant image. Thus, it is difficult to obtain an image including no defects.
As described above, when images are printed on both sides of a cloth using any conventional textile printing technique or apparatus in such a manner that after forming an image on the principal surface of the cloth and then the cloth is turned over and finally another image is printed on the back surface, the image formed on the back surface becomes inconsistent with the image formed on the principal surface due to deformation of the cloth caused by the expansion/contraction properties of the cloth (that is, it is difficult to achieve sufficiently high accuracy in registration between the images on both sides). Thus, the printing technique on cloths is used only to form an image on one surface. Therefore, the back side on which no image is printed looks whitish. This limits the applications of the printed cloths and it is impossible to increase their value.
As described above, any conventional textile printing technique cannot form images on both sides such that the images on both sides have the same image intensity and such that the images on both sides are coincident with each other.
Thus, it is an object of the invention to provide an image forming method and apparatus having a simplified construction, capable of printing a high-precision image with no distortion on a recording medium having expansion/contraction properties, such as a cloth.
According to an aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording medium using a recording head in accordance with image data, the apparatus comprising: conveying means for conveying the recording medium; evaluation means for evaluating the distortion of the recording medium conveyed by the conveying means; correction means for correcting the image data in accordance with the result of the evaluation made by the evaluation means; and image forming means for forming an image on the recording medium by driving the recording head in accordance with the image data corrected by the correction means.
According to another aspect of the present invention, there is provided a method of forming an image on a recording medium using a recording head in accordance with image data, the method comprising the steps of: conveying the recording medium; evaluating the distortion of the recording medium conveyed; correcting the image data in accordance with the result of the evaluation made in the evaluation step; and forming an image on the recording medium using the recording head in accordance with the image data corrected in the correction step.
Another object of the present invention is to provide a method and apparatus capable of forming a higher-precision image with no distortion even when an image is formed on a mixed fabric via a plurality of image forming operations using different types of dyes.
To achieve the above object, the invention provides an image forming apparatus for forming an image on a recording medium using a recording head in accordance with image data, the apparatus comprising: conveying means for conveying the recording medium; evaluation means for evaluating the distortion of the recording medium conveyed by the conveying means; correction means for correcting the image data in accordance with the result of the evaluation made by the evaluation means; control means for controlling the image forming process such that an image is formed a plurality of times on the recording medium in accordance with the same image data, and such that at least in one of the plurality of image forming processes, the evaluation means evaluates the distortion of the recording medium and then the correction means corrects the image data and finally an image is formed in accordance with the corrected image data.
The invention also provides a method of forming an image on a recording medium using a recording head, wherein the method includes: a first image forming step in which an image is formed on the conveyed recording medium in accordance with image data; conveying the recording medium; evaluating the distortion of the recording medium conveyed; correcting the image data in accordance with the evaluation result given by the evaluation means; and a second image forming step in which an image is formed on the recording medium using the recording head in accordance with the image data corrected in the correction step.
Another object of the present invention is to provide an image forming method and apparatus capable of forming high-precision images with high-quality colors including little color shading on both sides of a recording medium having expansion/contraction properties for use in special applications in such a manner that the images formed on both sides are coincident with each other.
Still another object of the present invention is to provide an image forming method and apparatus capable of forming an image from both side of a cloth such that a sufficiently large amount of dye ink can achieve the opposite side thereby ensuring that beautiful images which are suitable in particular for handkerchiefs or scarfs can be printed on both sides.
According to an aspect of the invention, to achieve the above objects, there is provided an image forming apparatus including: first recording means disposed at a location which allows the first recording means to face the principal surface of a recording medium, the first recording means serving to form an image on the surface of the recording medium by applying a recording agent, via a recording head, to the principal surface of the recording medium; first conveying means for conveying the recording medium to the first recording means; second recording means disposed at a location which allows the second recording means to face the back surface of the recording medium, the second recording means serving to form an image on the back surface of the recording medium by applying a recording agent, via a recording head, to the back surface of the recording medium; second conveying means disposed on an extension of the conveying path of the first conveying means, the second conveying means serving to receive the recording medium from the first conveying means and convey it to the second recording means; and both-side alignment controlling means for controlling the positions where images are formed so that the image formed on the back surface of the recording medium by the second recording means becomes coincident with the image formed on the principal surface of the recording medium by the first recording means.
According to another aspect of the invention, there is provided an image forming apparatus including: conveying means for conveying a recording medium; recording means disposed such that the first recording means faces the principal surface of the recording medium conveyed by the conveying means, the first recording means serving to form an image on the principal surface of the recording medium by applying a recording agent, via a recording head, to the principal surface of the recording medium; recording medium storing means disposed on an extension of the conveying path of the conveying means, the recording medium storing means serving to temporarily store the recording medium received via the conveying means while preserving the recording starting position; recording medium turning-over/conveying means for conveying the recording medium stored in the recording medium storing means from the recording starting position such that the back surface of the recording medium faces the recording means; back surface image forming means for transmitting image data converted in a mirror-symmetric fashion in the conveying direction to the recording means; and both-side alignment controlling means for controlling the positions where images are formed so that the image formed on the back surface of the recording medium conveyed by the recording medium turning-over/conveying means becomes coincident with the image formed on the principal surface of the recording medium.
According to still another aspect of the invention, there is provided a method of forming an image on a recording medium by applying a recording agent to the recording medium, the method including: a first image forming step in which an image is formed on one surface of the recording medium by applying a recording agent in accordance with image data; a conveying step in which the recording medium on which the image has been formed in the first image forming step is conveyed; an evaluation step in which the state of the recording medium conveyed in the conveying step is evaluated; a processing step in which the image data is processed in accordance with the result of the evaluation made in the evaluation step; and a second image forming step in which in accordance with the image data processed in the processing step an image is formed on the surface opposite to the surface on which the image has been formed in the first image forming step.
According still another aspect of the invention, there is provided an image forming apparatus for forming an image on a recording medium using a recording head, the apparatus including: conveying means for conveying a recording medium; evaluation means for evaluating the state of the conveyed recording medium; processing means for processing image data to be recorded, in accordance with the result of the evaluation; and recording process controlling means for controlling the image forming process such that an image is formed by the recording head on one surface of the recording means in accordance with image data, the state of the recording medium having the image formed on the one surface thereof conveyed by the conveying means is evaluated by the evaluation means, the image data is processed by the processing means in accordance with the result of the evaluation, and an image is formed by the recording head on the surface opposite to the surface on which the image has been formed.
By employing any of the image forming apparatus and/or image forming methods described above, it becomes possible to evaluate distortion which can occur in a recording medium having expansion/contraction properties such as a cloth when the recording medium is conveyed and thus it becomes possible to form a high-precision image at a correct position on the recording medium in accordance with image data corrected depending on the distortion detected.
Thus, the present invention provides an image forming apparatus and method capable of forming a high-precision image with a guaranteed high accuracy on a coth employed as the recording medium at low cost even when the cloth is conveyed in an expanded/contracted state.